• Title/Summary/Keyword: beer-spoilage lactic acid bacteria

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Rapid detection of beer-spoilage lactic acid bacteria: Modified hop-gradient agar with ethanol method

  • Hong, Lim Seok;Kim, Ji Hyeon;Kim, Wang June
    • Korean Journal of Food Science and Technology
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    • v.52 no.3
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    • pp.296-303
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    • 2020
  • Hop-resistant lactic acid bacteria (LAB) are well-known, major beer-spoilage bacteria. The hop-gradient agar containing ethanol (c-HGA+E) method has been used to examine hop-resistance of beer-spoilage LAB. However, the selection of beer-spoilage bacteria by the c-HGA+E method is either too selective or too inclusive. Furthermore, it is accompanied by a complicated experimental procedure, high-cost and time. To overcome these disadvantages, the modified hop-gradient agar with ethanol (m-HGA+E) method was developed. The most remarkable modifications were the shape of the petri dish and the inoculation method for bacteria. The efficiency and validation of the m-HGA+E approach were proven by the formation of colonies at different hop concentrations in the bottom layer, co-culture with the bacteriocin producer and by PCR detection of hop-resistant genes. This study demonstrated that m-HGA+E is a rapid, economical, and easy method to monitor potential hop-resistant beer-spoilage LAB during the beer brewing process.

Identification of a Prophage-encoded Abortive Infection System in Levilactobacillus brevis

  • Feyereisen, Marine;Mahony, Jennifer;O'Sullivan, Tadhg;Boer, Viktor;van Sinderen, Douwe
    • Microbiology and Biotechnology Letters
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    • v.48 no.3
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    • pp.322-327
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    • 2020
  • Abortive infection systems (Abi) are phage resistance systems that can be prophage-encoded. Here, two genes encoding an Abi system were identified on a prophage sequence contained by the chromosome of the Levilactobacillus brevis strain UCCLBBS124. This Abi system is similar to the two-component AbiL system encoded by Lactococcus lactis biovar. diacetylactis LD10-1. The UCCLBBS124 prophage-derived Abi system (designated here as AbiL124) was shown to exhibit specific activity against phages infecting L. brevis and L. lactis strains. Expression of the AbiL124 system was shown to cause reduction in the efficiency of plaquing and cell lysis delay for phages of both species.